NL1028938C2 - Mass flow meter of the Coriolist type. - Google Patents

Description

Mass flow meter of the Coriolistvpe

The invention relates to a ryiass flow meter of the Coriolis type, with a tube forming a loop through which a medium 5 flows during operation and with shock means (excitation means) for causing the loop to vibrate during operation about a primary axis of rotation. in hpt plane of the loop.

Such a mass flow meter is described in USP 4 658 657.

The known mass flow meter has a non-closed loop-shaped tube (half-turn) which on one side forms a transverse arm which is connected to two side arms which are clamped on a opposite beam on the opposite side. This is mounted in a support so that it can rotate about a central axis in the plane of the loop. For an oscillating rotation (vibration) of the mounting beam with a loop around the central axis, an electromagnetic shock system ensures that it compresses with the (magnetic) mounting beam. When a medium flows through the loop rotating about the central axis, coriolis forces are generated in the transverse arm lying transversely to the axis of rotation, which results in a vibration of the loop about an axis perpendicular to the impulse rotatip axis. This vibration, which is proportional to the flow, is superimposed on the fundamental oscillation and leads to a phase shift between the oscillations that carry out the cross-arm ends. The phase difference is proportional to the coriplis force, and therefore to the flow.

A disadvantage of the known system, however, is that extra mass is added by means of the mounting beam used for triggering the loop. This prevents the change of the pan burst frequency with the density of the medium flowing through the tube, whereby the measurement of the density (an additional property of a Coriolis flowpeter) becomes less accurate.

The invention is based, inter alia, on providing a flow meter with an impulse system with which more accurate measurement of the density is possible.

To this end, the mass flow meter of the type mentioned in the preamble is characterized in that the loop follows a substantially circular, mechanically closed path, that the loop is connected to a flexible supply pipe and a flexible discharge pipe for the flowing medium, and that the The loop is resiliently suspended from a frame via the flexible supply and discharge pipes, such that 1 0 2 J1 9 3 «! 2 the suspension allows a movement about two perpendicular axes in the plane of the loop, one for the impact movement and one for the Coriolis movement that occurs when a medium flows through the tube.

According to the invention, the mechanically closed loop-shaped tube is resiliently suspended via the supply and discharge tube, which together function as a flexible connecting element. That is, the supply and discharge pipes are flexible and torsional to the extent (twistable) to a greater or lesser extent, and therefore act as a spring element. This suspension allows movement about two perpendicular axes in the plane of the loop, one for the impact movement and one for the coriolis movement.

A mass flow meter with a loop-shaped tube suspended in such a way has an increased sensitivity in that the supply and discharge tubes have the greatest possible free spring length and, in particular when they extend parallel and close to each other, the suspension stiffness of the loop is minimized. 15 is at a given tube diameter. Moreover, the advantage of attaching the supply and discharge pipes to the frame next to each other is that the temperature sensitivity of the flow meter is lower than in the case that the fixing points are far apart.

As will be explained in more detail below, different variants of the supply and discharge pipe parts are possible, each with its own advantages. A practical and mechanically preferable embodiment is, for example, that in which the loop with the supply and discharge tube consists of one piece.

Irrespective of the further embodiment, it is important that the supply and discharge pipes are attached to the frame at a predetermined distance from the place where they are connected to the loop by means of fastening means, by which distance their free path length is determined .

The supply and discharge tube can lie in the plane of the loop or outside the plane of the loop. However, the more they lie in the plane of the loop, the more favorable that is. If they are in the plane of the loop, they may be wholly or partially within the loop. Alternatively, they may be entirely outside the loop, for example, in line in a plane transverse to the loop, in line in the plane of the loop, parallel in a plane that makes an angle with the plane of the loop, or parallel in the plane plane of the loop, but outside the loop.

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A preferred form is characterized in that the supply and discharge pipes are parallel, close to each other over their free path lengths, because then the torsional rigidity is lower, and preferably has a maximum free length up to the fastening means, because this lowers the flexural rigidity. A maximum free path length 5 can be realized by attaching the feed and discharge tube to mounting means outside the loop on the frame.

As will be explained in more detail below, the loop-shaped tube can be struck in the so-called twist or rotatip mode, or in the so-called parallel or swing mode. In the context of the invention, the twist mode is preferred, in particular if it takes place about an axis of rotation in the symmetry plane of the loop.

An inventive ring shape which is advantageous in terms of sensitivity is characterized in that the loop forms a rectangle with two parallel lateral tubes, a first transverse tube connected to first ends of the lateral tubes, and two second transverse tubes connected on one side to the second ends of the lateral tubes. pipes are connected and on the other side to the supply and discharge pipes respectively.

A very compact embodiment of the above concept is characterized in that the supply and discharge pipes run close to each other at the plane of the loop and within the loop, the supply and discharge pipes being located on either side of a symmetrical axis of extend the loop and are attached to the frame at a position closer to the first cross tube than at the second cross tubes. More in particular, the free path gap of the supply and discharge tube is at least 50% of the height of the loop in the direction parallel to the supply and discharge tube. For the loop-shaped tube that forms a rectangle, this means that the free path length of the supply and discharge tubes is at least 50% of the length of the lateral tubes.

The loop should preferably be mechanically closed. To that end, a first embodiment is characterized in that the second transverse tubes are mechanically connected to each other near their connection to the supply and discharge tubes.

A second embodiment is characterized in that the supply and discharge pipes run parallel and close to each other over their free path length and are mechanically connected to each other at least over a part of their free path length.

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The striking (vibrating) of loop-shaped tube of the mass flow meter according to the invention can take place in various ways. For example, with the help of a magnetic disk glued onto the tube and an air-coil electromagnet. However, the present loop is itself a very light object, and if shock means are attached to it, it takes extra energy to make the loop resonant. Therefore, an impact technique is preferably used which makes it unnecessary to add additional components to the loop.

In this context, an embodiment is characterized in that the excitation means comprise means adapted to generate an electric current in the wall of the tube, and magnetic means which generate a magnetic field transversely of the direction of flow in the tube wall for use in combination applying electromagnetic forces (so-called Lorentz forces) to the tube with the current through the tube in order to cause the tube to rotate about one of the perpendicular axes. Lorentz forces are complaints that are generated when an electric current moves through a magnetic field.

In this connection, a first embodiment is characterized in that the magnet means comprise a permanent magnet yoke with one air gap through which a tube part runs. With this a so-called parallel or swing impact mode can be realized-

An embodiment for realizing a so-called rotation or twist impulse mode is characterized in that the magnet means comprise a permanent magnetic magnet yoke with two air gaps through which a tube part runs, in which air gap prevails oppositely directed magnetic fields.

To measure the effect of the Coriolis forces, two sensors for measuring displacements of two points of the tube are preferably arranged as a function of time on either side of the primary axis of rotation (the stub axis). When there is little space, such as for example in the case of a tube with a delta shape, it is of advantage when the magnetic yoke has a central opening between the air gaps and that the sensors are arranged in the opening.

With a tube that forms a rectangular loop, there is more room to arrange the sensors and the magnetic yoke as favorably as possible. According to an embodiment, with a tube forming a rectangular loop, the magnetic yoke is arranged on one side of the rectangular loop and the sensors are on the opposite side.

The invention will be explained in more detail with reference to the drawing, which shows some exemplary embodiments of the invention.

Fig. 1 shows a front view of a Qoriolis flow meter according to the invention;

Fig. 2 shows a perspective view of the flow meter of Fig. 1; Fig. 3 shows a perspective view of the loop-shaped tube used in the flow meter of Fig. 1 and 2;

4A and B show front views and FIG. 4C-F show perspective views of alternative embodiments of the suspension of the loop-shaped tube of Fig. 3; FIG. 5 and 6 show front views of alternative embodiments of the loop-shaped tube of Fig. 3.

Description of status

Fig. 1 shows a flow meter 1 of the Corioli type with a loop-shaped tube 2 curved in the form of a rectangle, which pin follows a substantially circumferential path (forms an almost complete turn) and a - flexible - supply pipe 3 and a - flexible - discharge pipe 4 for a flowing medium. The loop 2 and the supply and discharge tubes 3,4 are preferably parts of one and the same tube. The tube 2 as a whole is bent in the shape of a rectangle, but the corners run round to allow bending in this shape. Via a supply and discharge block 20 the supply pipe 3 is connected to a supply pipe 6 and the discharge pipe 4 is connected to a discharge pipe 7. In this embodiment the supply and discharge pipe 3.4 extend within the loop 2 and are of fasteners 12 attached to frame 13 (clamped). The attachment is at such a location that the free path length of the supply and discharge tube 3.4 (the part of the supply and discharge tube 3.4 between the connection of the second transverse tube parts 2a and 2b and the location of consent to fastener 12) is at least 50%, and preferably at least 60%, of the length of the lateral 1028938 6 pipe sections 2d, 2e. The flexible supply and discharge tube 3,4 do not form part of the loop shape 2, but provide a flexible attachment of the loop 2 to the frame 13. The loop 2 is therefore suspended as "flexible" via the supply and discharge tube The loop 2 and the supply and discharge tubes 3,4 can advantageously be made from one piece of tube, which can for instance be a stainless steel tube with an outer diameter of approximately 0.7 mm, and a wall thickness of approximately 0 Depending on the outside dimensions of the loop 2 and the pressure that the pipe must be able to withstand (for example 100 bar), the outside diameter of the pipe will generally be smaller than 1 mm and the wall thickness 0.2 10 mm or smaller.

The loop-shaped tube 2 is shown in further detail in Fig. 3 in which the same reference numbers are used for the same components as in Fig. 1. The tube 2 consists of a substantially rectangular framework of two parallel lateral tubes 2d and 2e, a first transverse tube 2c which is connected to first (lower) ends of the lateral tubes 2d and 2e, and two second transverse tubes 2a and 2b connected to one are connected on the one side to the second (upper) ends of the lateral tubes and on the other side to the centrally recirculating supply and discharge tubes 3 resp. 4. The rectangular loop 2 preferably has rounded corners. The tubes 3 and 4, which run close to each other on either side of, and symmetrical to, the main symmetry axis S of the loop 2 are fixed to the fastening means 12, for example by clamping or by means of soldering or welding. that is itself attached to base plate 13.

In FIG. 3 shows, by way of example, a cavity 14 in fastening means (block) 12 in which the tubes 3 and 4 are fixed. The supply and discharge tubes 3, 4 are flexible and function as it were as a suspension spring for the loop 2. This suspension allows movement of the loop 2 about both the main symmetry axis S and about a second in the plane of the loop 2 located axis S 'which is perpendicular to the main symmetry axis S.

In order to make the loop 2 mechanically closed (i.e., the start and end points of the loop are directly or indirectly mechanically connected to each other), the tubes 3 and 4 are preferably over the range of their free path length with connected to each other, for example by welding them together or soldering them together. In FIG. 3, by way of example, some connection locations are indicated by reference numeral 15 with 1028938 7.

An alternative is to connect the cross tubes 2a and 2b with each other, and optionally with the supply and discharge tubes 3 and 4. For example by attaching them to a support element 16 at the place where they come close together. ! The connection between the second transverse tubes 2a, 2b and between the supply and discharge tubes 3,4 is important for creating a mechanically closed loop in order to obtain the correct vibration modes during operation.

For a good spring action, the tubes 3 and 4 preferably have as large a possible free path as possible. More particularly, d is preferably greater than 0.5 x the length D of the lateral tubes 2d and 2e. The positioning of the fastening means 12 is thus closer to the first cross tube 2c than to the second cross tubes 2a, 2b.

In the exemplary embodiment of Fig. 3, the supply pipe 3 and the discharge pipe 4 bend past the fastening means 12 over the surface of the loop 2, bending around the first transverse pipe 2c, in order to be connected to feed and discharge pipes. In order to facilitate that connection, they preferably separate from each other. This can be seen more clearly in Fig.2. I

In FIG. 4, alternatives are shown for arranging and clamping the inlet and outlet pipes, which alternatives all use the suspension principle presented with reference to FIG. 3. In the alternatives of Fig. 4, extra slackness is added to the loop attachment by placing the attachment points further away.

Fig. 4A shows a substantially rectangular loop-shaped tube 21 with apn and discharge tubes 20, 21 extending inside and in the plane of the loop, which laterally run away from a predetermined point to different sides. The tubes 20, 21 are clamped (fixed) at securing locations 22, 23 that lie within the loop. By placing the fixing points further away in relation to the situation in Fig. 3, extra slackness is added to the resilient suspension. The tubes 20, 21 can extend beyond the clamping positions 22, 23 with a bend over the lateral tubes 24, 25 of the tubular loop 21, or (with a right-angled bend) can be pivoted backwards.

Fig. 4B shows a substantially rectangular loop-shaped tube 26 with parallel supply and discharge tubes extending within and in the plane of the tube 1028938 8 27.28 which run from a predetermined point with an extra bend to their respective mounting locations. The tubes 27, 28 are clamped in places 29 and 30. In this way, the attachment places are set aside even further than in Fig. 4A.

If one would like to extend the free path length of the supply and discharge pipes beyond the lower transverse pipe (compared with Fig. 2) by bending them out of the plane of the loop (over the lower transverse pipe), it is detrimental to the dynamic spring properties. This problem is solved by the construction of Fig. 4C.

Fig. 4C shows a substantially rectangular loop-shaped tube 31 with supply and discharge tubes 32,33 running close together in one plane. The tubes 32, 33 are clamped by means of the fastening means 34 which is located outside the loop 31. The tubes 32,33 show no kinks, because the lower transverse tube 35 of the loop 31 is provided outwards.

Fig. 4D shows a substantially rectangular loop-shaped tube 36 with supply and discharge tubes 37, 38 which first run in the plane of the loop 36, then split away from the plane of the loop 36 in opposite directions. The tubes 37, 38 are clamped at a predetermined distance outside the plane of the loop 36 at locations 39 and 40 to increase the free path length.

! Fig. 4E relates to an alternative to the construction of Fig. 4D and shows a substantially rectangular loop-shaped tube 41 with supply and discharge tubes 42, 43 which do not first run in the plane of the loop, as in Figs. 4D, but directly split away from the plane of the loop 41 in opposite directions. The tubes 42, 43 are clamped outside the plane of the loop 41 at positions 44 and 45.

FIG. 4F shows a substantially rectangular loop-shaped tube 46 with supply and discharge tubes 47, 48 which run directly out of the plane of the loop 46 in the same direction. The, preferably parallel, drain and drain pipes 47, 48 are clamped in place 49 outside the plane of the loop 46. This construction is an alternative to the construction of FIG. 4E and provides greater rigidity, especially when the tubes 47, 48 are mechanically connected to each other.

With the variants where the clamping positions lie outside the plane of the loop (Fig. 4D, 4E, 4F) it is advantageous if they are symmetrical with respect to the plane of the loop.

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The embodiments described above show a rectangular loop. However, I

ter, as long as the loop forms a (substantially) closed coil, variants of the rectangular loop shape can also be used. A few of these, all resiliently suspended via supply and discharge tubes located within the loop, are shown in front view in Fig. 5.

Fig. 5A shows a front view of a polygonal (in this case eight-dimensional)

loop, but hexagonal or more than eight angles is also applicable).

Fig. 5B. shows an elliptical loop 51.

FIG. 5C shows a diamond-shaped loop 52. I

Fig. 5D shows a trapezoidal loop 53. i

With the loop shapes shown in Fig. 5, the resilient part of the supply and discharge pipes is entirely within the loop. But the pnag is also partially outside, as in Fig. 4C and 4D, or completely outside, as in Fig. 4E and Fig. 4F. The sensitivity of mass flow meters with the loop shapes shown in ϊη Fig. 5 differs little from each other. With the same outside dimensions, however, the rectangular shape of Fig. 3 gives the greatest sensitivity.

FIG. 6A and 6B show loop-shaped tubes 54 and 61 according to the invention which are formed in the form of a delta and can be considered as variants on the rectangular tube of Fig. 3. Loop-shaped tube 54 (Fig. 6A) has a supply tube 55 which is connected to the loop near the starting point 56 of the loop 54. From the beginning point 56, incoming flow flows through a first sloping side of the delta shape, then the base side 60 and finally a second sloping side of the delta shape. At end-point 58, delta-shaped tubes 54 are connected to a discharge tube 57. The supply and discharge tubes 55, 57 extend parallel, close to each other in the plane of the loop 54 within the loop 54 and are attached to a frame (not shown) attached via fastening means 59. Hereby a resilient suspension of the loop 54 is realized which is comparable to that of the loop 2 in Fig. 3. At the transition from the base side 60 to each of the oblique sides, the tube 54 may be provided with protrusions in the form of "ears".

Mutatis mutandis, the same applies to the loop-shaped tube 61 shown in Fig. 6B, which is also bent in the form of a delta. In that case, the supply and discharge tubes 62, 64 extend parallel, close to each other in the plane of the loop 61 outside the loop 61, whereby the free length of the lines formed by the supply and discharge tubes 62, 64 is formed. spring can be larger than in the construction of FIG.

6A. The supply and discharge tube 62, 64 are attached on the one hand to a frame (not shown) via a fastening means 66 and on the other hand to the starting point 63 and the end point 65 of the delta-shaped tube 61.

In order to mechanically close the loop-shaped tubes 54 and 61 shown in Figs. 6A and 6B, a mechanical connection can be made between the starting points 56.63 and the end points 58.65 of the respective loops 54 and 61. An alternative is to and drain pipes 55.57 resp. 62,64 to be mechanically joined over at least a part of their free path length, for example by welding or soldering. The mechanical connection suppresses the occurrence of natural frequencies that can disturb the measurement.

The closed delta-shaped tubes according to the invention can alternatively be provided with a double loop instead of with a single loop. Depending on the embodiment, both an equal and an opposite flow direction are possible in the two loop parts.

The striking (vibrating) of the loop-shaped tube of the mass flow meter according to the invention can take place in various ways. For example, with the help of a magnetic disk stuck to the tube and an air coil electromagnet. However, the present loop is a very light object in itself and if impact means are attached to it, it takes extra energy to make the loop resonant. Therefore, in Figs. 1 and 2, special shock means are shown which do not require the addition of additional components to the loop.

Impact means for causing the loop 2 to rotate about the main symmetry axis S (in this case the primary, or impact) axis of rotation comprises in the construction of Fig. 1 and of Figs. 2 (in which the same reference numerals are used as in Fig. 1) a permanent magnetic yoke 8 mounted on the frame 13 with two slits 9 and 10 through which parts 2a and 2b (referred to above as the second transverse tubes) run of the loop-shaped tube 2, as well as means to introduce an electric current into the tube 2. In the present case these are means for inducing current in the tube 2.

The current is induced in the tube by means of two transformers 17, 17a each provided with a coil 18a and 18b respectively, through which the respective tube parts 2c and 2d pass. Due to the combination of the magnetic fields generated in the gaps 9 and 10 of the permanent magnetic yoke 8, opposed to the direction of flow and oppositely directed magnetic fields and an (alternating) current induced in the tube 2, a torque is exerted on the tube so that it 5 the axis S (oscillating) starts to rotate (vibrate, so-called twist mode). When a medium flows through the tube, the tube yawns under the influence of Coriolis forces to rotate about an axis S ", transverse to the ps S (so-called swing mode). In operation, the (sinusoidal) displacements of points of tube part 2c, which are representative of the flow, are detected with the aid of a first sensor 11a, a second sensor 1 * | b, and, optionally, a third sensor 11c. The first and second sensors are arranged on either side of the first axis of rotation S. The third sensor 11c can be used for correction purposes. The sensors may, for example, be electromagnetic, inductive, capacitive, or ultrasonic in nature. However, optic sensors have been chosen in this case. The sensors 11a, 11b, and 11c (Fig. 1 and Fig. 2) each comprise a U-shaped housing mounted on the frame 13 with a light source (for example an LED) in one leg of the U and in the other a light measuring cell disposed opposite the light source (for example a phototransistor). The transverse tube 2c can move between the legs of the U-shaped sensor housings 11a, 11b (and if present: 11c).

Briefly, the invention relates to a mass flow meter of the Coriolist type, with a tube forming a plotted loop through which a medium flows in operation and with excitation means for causing the loop to rotate oscillating in rotation about a rotation qs during operation. The loop has a starting point and an end point. The start and end points are closely matched and are respectively connected to a flexible feed tube and a flexible drain tube which preferably run parallel and close to each other. The loop is resiliently suspended from the flow meter frame via the flexible supply and discharge tubes, which preferably consist of one piece with the tube of the loop.

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Claims (17)

A mass flow meter of the Coriolist type, with a tube forming a loop through which a medium flows in operation and with impact means for causing the loop to vibrate in operation about an axis of rotation in the plane of the loop, characterized in that that the loop follows a substantially circumferential, mechanically closed path, that the loop is connected to a flexible supply pipe and a flexible discharge pipe for the fluid medium, and that the loop is resiliently suspended from a frame via the flexible supply and discharge pipes, a and another such that the suspension allows movement about two perpendicular axes in the plane of the loop, one for the pan-shot movement and one for the coriolis movement that occurs when a mecjium flows through the tube. A mass flow meter according to claim 1, characterized in that the loop with the supply and discharge tube consists of one piece. A mass flow meter as claimed in claim 1, characterized in that the supply and discharge pipes are fixed to the frame at a predetermined distance from the place where they are connected to the loop by means of fastening means, by which distance their free path length is determined determined. A mass flow meter according to claim 3, characterized in that the supply and discharge pipes are parallel and close to each other over their free path lengths and are attached to the fastening means next to each other. 5. A mass flow meter as claimed in claim 1, wherein the loop forms a rectangle with two parallel lateral tubes, a first transverse tube connected to first ends of the lateral tubes, and two second transverse tubes connected on one side to the second ends of the lateral tubes. pipes are connected and on the other side to the supply and discharge pipes respectively. 6. A mass flow meter as claimed in claim 5, characterized in that the supply and discharge pipes run close to each other in the plane of the loop and within the loop, the supply and discharge pipes being on either side of a symmetry. extend the axis of the loop and are attached to the 1028938 frame at a position closer to the first cross tube than in the second cross tubes. A mass flow meter as claimed in claim 1, characterized in that the impact means impact the loop in a twist impact mode. 8. A mass flow meter as claimed in claim 3, characterized in that the free path length of the supply and discharge tube amounts to at least 50% of the height of the loop viewed in the direction parallel to the supply and discharge tube. Mass flow meter according to claim 5, 10, characterized in that the free path length of the supply and discharge pipes is at least 50% of the length of the lateral tubes. A mass flow meter according to claim 5, characterized in that the second transverse tubes are mechanically connected to each other near their connection to the supply and discharge tubes. A mass flow meter according to claim 1 or 2, characterized in that the supply and discharge pipes run parallel and close to each other over their free path length and are mechanically connected to each other over at least a part of their free path length. 12. A mass flow meter as claimed in claim 1, characterized in that the excitation means comprise means adapted to generate an electric current in the wall of the tube, and magnetic means that generate a magnetic field transversely of the direction of flow in the tube wall to in combination with the current through the tube exerting Lorentz forces on the tube, A mass flow meter as claimed in claim 12, characterized in that the magnet means comprise a permanent magnet yoke with one air gap through which a tube part runs. 14. A mass flow meter according to claim 12, characterized in that the magnet means comprise a permanent magnetic magnet yoke with two air gaps through which a tube part runs, in which air gaps prevail oppositely directed magnetic fields. A mass flow meter according to claims 1 and 13, characterized in that two sensors for measuring displacements of 1028938 are arranged two points of the tube as a function of time on either side of the primary axis of rotation. A mass flow meter according to claim 14, characterized in that the magnetic yoke has a central opening between the air gaps and that the sensors are arranged in the opening. A mass flow meter as claimed in claim 12, characterized in that the tube forms a rectangular loop, that the magnetic yoke is arranged on one side of the rectangular loop and the sensors on the opposite side. 1028938